Stress has become a social issue because of its growing deleterious effect on performance, quality of life and health. Some attempts have been done to define stress indexes, but are more related to stress reactivity and recovery, e.g. during specific relaxation exercises and not to a real-life level. Several stress management devices have been developed that rely on the measurement of at least one vital parameter and give feedback to the user about changes of that parameter or a stress index into which it is translated. The procedure is called biofeedback. By observing the direct feedback, the user can learn to control his bodily functions in a way that is favorable in some context. Biofeedback devices for stress management employ measurements of various vital parameters that can easily be measured, like ECG, skin temperature, skin conductivity (galvanic skin response) and heart rate (often a finger- or ear-clip containing an optical heart rate measurement). The idea is in any case that by displaying the measurement results or some kind of index into which the measurement results are translated, the user learns to control his bodily functions such that he gets into a more relaxed state. However, the overall stress level is difficult to assess and is characterized by a pronounced variability between subjects. Stress also depends largely on the individual perception, which can vary from day to day. That is why the proposed stress index depends on several parameters, including outputs of a questionnaire and a measurement protocol.
Most of the stress management devices are limited to monitoring a single parameter. For example, assessment of the user's condition and instructions for relaxation exercise are only based on the measured HRV. Besides heart rate variability, other physiological parameters have shown to be related to the level of stress/relaxation, such as the respiration (rate and volume/amplitude). The users of these devices are left to themselves to find motivation, to implement the plans for achieving their targets, to monitor progress and to find and suggest solutions when problems arise. However, traditional practitioners do not have the time, the infrastructure, the resources, the training, and reimbursement possibilities to address the needs of those people.